Black holes, quantum information, and unitary evolution

TL;DR

This paper proposes a framework where unitarity is fundamental in quantum mechanics, allowing for non-locality to describe black hole information transfer and the emergence of spacetime in quantum gravity.

Contribution

It introduces a Hilbert space-based approach to model black hole information transfer with minimal departure from field theory, emphasizing approximate locality and tensor decompositions.

Findings

Unitarity can be maintained with non-local dynamics in black hole physics.

Approximate locality can be described via tensor decompositions of Hilbert spaces.

A framework for quantum gravity and emergent spacetime is proposed.

Abstract

The unitary crisis for black holes indicates an apparent need to modify local quantum field theory. This paper explores the idea that quantum mechanics and in particular unitarity are fundamental principles, but at the price of familiar locality. Thus, one should seek to parameterize unitary evolution, extending the field theory description of black holes, such that their quantum information is transferred to the external state. This discussion is set in a broader framework of unitary evolution acting on Hilbert spaces comprising subsystems. Here, various constraints can be placed on the dynamics, based on quantum information-theoretic and other general physical considerations, and one can seek to describe dynamics with "minimal" departure from field theory. While usual spacetime locality may not be a precise concept in quantum gravity, approximate locality seems an important ingredient in physics. In such a Hilbert space approach an apparently "coarser" form of localization can be described in terms of tensor decompositions of the Hilbert space of the complete system. This suggests a general framework in which to seek a consistent description of quantum gravity, and approximate emergence of spacetime. Other possible aspects of such a framework -- in particular symmetries -- are briefly discussed.